Temperature dependency of miniature end plate currents from the extraocular muscle of Antarctic teleost fishes

The effects of temperature on the decay phase of post-synaptic currents were examined to determine the extent of temperature compensation in the inferior oblique extraocular muscles of four Antarctic fishes (Trematomus bernacchii, Trematomus pennellii, Trematomus hansoni, and Pagothenia borchgrevinki, Family Nototheniidae). At ambient temperatures, different fish produce miniature end plate currents (MEPCs), which vary in duration and rate of decay. Low temperatures normally prolong MEPCs, however, Antarctic fishes were found to produce MEPCs of significantly shorter duration than predicted (based on back-extrapolation of temperate fish data to sub-zero temperatures). Notothenioid decay time constants were approximately 500 μs faster than their temperate counterparts, extrapolated to −2°C, suggesting that the difference is consistent with temperature compensation in the neural-systems of Antarctic fish. Results presented here conform the hypothesis that post-synaptic MEPCs of Antarctic fish exhibit temperature compensation, an adaptive feature that has permitted the successful radiation throughout the Southern Ocean.     

Comparison of excitatory currents activated by different transmitters on crustacean muscle. I. Acetylcholine-activated channels

The properties of acetylcholine-activated excitatory currents on the gm1 muscle of three marine decapod crustaceans, the spiny lobsters Panulirus argus and interruptus, and the crab Cancer borealis, were examined using either noise analysis, analysis of synaptic current decays, or analysis of the voltage dependence of ionophoretically activated cholinergic conductance increases. The apparent mean channel open time (tau n) obtained from noise analysis at -80 mV and 12 degrees C was approximately 13 ms; tau n was prolonged e-fold for about every 100-mV hyperpolarization in membrane potential; tau n was prolonged e- fold for every 10 degrees C decrease in temperature. Gamma, the single- channel conductance, at 12 degrees C was approximately 18 pS and was not affected by voltage; gamma was increased approximately 2.5-fold for every 10 degrees C increase in temperature. Synaptic currents decayed with a single exponential time course, and at -80 mV and 12 degrees C, the time constant of decay of synaptic currents, tau ejc, was approximately 14-15 ms and was prolonged e-fold about every 140-mV hyperpolarization; tau ejc was prolonged about e-fold for every 10 degrees C decrease in temperature. The voltage dependence of the amplitude of steady-state cholinergic currents suggests that the total conductance increase produced by cholinergic agonists is increased with hyperpolarization. Compared with glutamate channels found on similar decapod muscles (see the following article), the acetylcholine channels stay open longer, conduct ions more slowly, and are more sensitive to changes in the membrane potential.     

Properties of miniature postsynaptic currents during depolarization-induced release at a cholinergic neuroneuronal synapse

1. Miniature postsynaptic currents were analyzed at an inhibitory cholinergic neuroneuronal synapse in the buccal ganglion of Aplysia. Under double voltage-clamp, it was possible to induce postsynaptic currents by long-duration depolarizations of the presynaptic neuron and to analyze these as the linear summation of individual miniature postsynaptic currents (MPSCs). The amplitude of these miniature currents (imin) was calculated from the ratio of the variance of the noise (E2) to the mean of the postsynaptic current (Im), according to Campbell's theorem, with imin = 2E2/Im. Their decay time (tau min) was obtained from the cutoff frequencies of the power spectra obtained from the noise. 2. Neither the conductance nor the decay time of MPSCs was voltage dependent. However, imin appeared to decrease when the quantal content of the response increased. Meanwhile, tau min increased slightly with Imin. 3. Carbamylcholine was injected into the neuropile and this led to a decrease in imin and a slight increase in tau min. 4. Power spectra obtained after the application of inhibitors of acetylcholinesterase (AChE), with or without curare, suggested that acetylcholine (ACh) does not accumulate during large depolarizations. 5. The possible origin of the nonlinear relationship between the variance and the mean of the postsynaptic currents is discussed.     

Functional characterization of parvalbumin from the Arctic cod (Boreogadus saida): similarity in calcium affinity among parvalbumins from polar teleosts

Calcium dissociation constants (KD) were measured as a function of temperature for parvalbumin, a small acidic protein expressed abundantly in fast-twitch muscle, from the Arctic cod (Boreogadus saida) and compared to values previously determined for Antarctic and temperate zone teleosts. Estimates of KD were derived independently from fluorometric titrations and calorimetry. In addition, the primary structure of B. saida parvalbumin was determined. Calcium KDs for parvalbumin from B. saida were fundamentally similar to those for parvalbumins from Antarctic species (6.68+/-0.59 nM and 7.77+/-0.72 nM at 5 degrees C, respectively), but significantly different from temperate zone species (1.35+/-0.28 nM at 5 degrees C). However, estimates of KD for B. saida parvalbumin at 5 degrees C closely matched values for temperate zone fish at 25 degrees C (6.54+/-0.56 nM), recapitulating the prior observation that calcium affinity of parvalbumin is conserved at the native temperature of teleost fish. Full sequence of B. saida parvalbumin was generated using reverse-phase HPLC and RACE-PCR. The Arctic parvalbumin showed 83% homology to a carp parvalbumin. None of the 16 total substitutions between the two parvalbumins resided in the cation binding sites of the protein, indicating that the structural locus of the thermal sensitivity of function lies outside the active regions.     

Effects of ammonium ions on endplate channels

Miniature endplate currents, recorded from voltage-clamped toad sartorius muscle fibers in solutions containing ammonium ions substituted for sodium ions, were increased in amplitude and decayed exponentially with a slower time constant than in control (Na) solution. The peak conductance of miniature endplate currents was also greater in ammonium solutions. The acetylcholine null potential was - 2.8 +/- 0.8 mV in control solution, and shifted to 0.9 +/- 1.6 mV in solutions in which NH4Cl replaced half the NaCl. In solutions containing NH4Cl substituted for all the NaCl, the null potential was 6.5 +/- 1.3 mV. Single channel conductance and average channel lifetime were both increased in solutions containing ammonium ions. The exponential relationship between the time constant of decay of miniature endplate currents or channel lifetime and membrane potential was unchanged in ammonium solutions. A slight but consistent increase in peak conductance during miniature endplate currents and single channel conductance was seen as membrane potential became more positive (depolarized) in both control and ammonium solutions. Net charge transfer was greater in ammonium solutions than in control solution, whether measured during a miniature endplate current or through a single channel. The results presented here are consistent with an endplate channel model containing high field strength, neutral sites.     

Voltage clamp study of fast excitatory synaptic currents in bullfrog sympathetic ganglion cells

Excitatory postsynaptic currents (EPSCs) have been studied in voltage- clamped bullfrog sympathetic ganglion B cells. The EPSC was small, rose to a peak within 1-3 ms, and then decayed exponentially over most of its time-course. For 36 cells at --50 mV (21-23 degrees C), peak EPSC size was --6.5 +/- 3.5 nA (mean +/- SD), and the mean decay time constant tau was 5.3 +/- 0.9 ms. tau showed a small negative voltage dependence, which appeared independent of temperature, over the range -- 90 to --30 mV; the coefficient of voltage dependence was --0.0039 +/- 0.0014 mV-1 (n = 29). The peak current-voltage relationship was linear between --120 and --30 mV but often deviated from linearity at more positive potentials. The reversal potential determined by interpolation was approximately --5 mV. EPSC decay tau had a Q10 = 3. The commonly used cholinesterase inhibitors, neostigmine and physostigmine, exhibited complex actions at the ganglia. Neostigmine (1 X 10(-5)M) produced a time-dependent slowing of EPSC decay without consistent change in EPSC size. In addition, the decay phase often deviated from a single exponential function, although it retained its negative voltage dependence. With 1 x 10(-6) M physostigmine, EPSC decay was slowed by the decay phase remained exponential. At higher concentrations of physostigmine, EPSC decay was markedly prolonged and was composed of at least two decay components. High concentrations of atropine (10(-5) to 10(-4) M) produced complex alterations in EPSC decay, creating two or more exponential components; one decay component was faster and the other was slower than that observed in untreated cells. These results suggest that the time-course of ganglionic EPSC decay is primarily determined by the kinetics of the receptor-channel complex rather than hydrolysis or diffusion of transmitter away from the postsynaptic receptors.     

Temperature sensitivity of calcium binding for parvalbumins from Antarctic and temperate zone teleost fishes

Parvalbumin (PV) is a soluble calcium-binding protein that is especially abundant in fast-twitch muscles of fish and other lower vertebrates. Despite its prevalence in ectothermic taxa, few data address the effects of temperature on PV binding function. In this study, calcium dissociation constants (KD) were measured as a function of temperature (0-25 degrees C) for PV from two Antarctic (Gobionotothen gibberifrons and Chaenocephalus aceratus) and two temperate zone fish species (Cyprinus carpio and Micropterus salmoides). Measurements by fluorometric competitive binding assay show that KD values for PVs from the Antarctic species were significantly higher at all assay temperatures and were less sensitive to temperature relative to carp and bass. However, estimates of KD are fundamentally similar for PVs from the Antarctic and temperate zone species when examined at their native physiological temperature. Variation in pH and ionic strength within a physiologically relevant range had only modest effects on KD. Thermodynamics of calcium binding to PV from G. gibberifrons and C. carpio was measured by isothermal microcalorimetry. When measured at 15 degrees C, the Gibbs free energy change (deltaG) was significantly greater for calcium binding to PV from G. gibberifrons than from carp (-43.4+/-1.5 kJ mol(-1) and -46.6+/-3.0 kJ mol(-1), respectively), and the relative contribution of entropy to deltaG for calcium binding to PV from the Antarctic species was about twice that of carp (deltaS=16.0+/-0.8 J degrees C(-1) mol(-1) for G. gibberifrons; deltaS=7.5+/-0.8 J degrees C(-1) mol(-1) for C. carpio).     

Conformational exchange on the microsecond time scale in alpha-helix and beta-hairpin peptides measured by 13C NMR transverse relaxation

13C-NMR relaxation experiments (T(1), T(2), T(1)(rho), and NOE) were performed on selectively enriched residues in two peptides, one hydrophobic staple alpha-helix-forming peptide GFSKAELAKARAAKRGGY and one beta-hairpin-forming peptide RGITVNGKTYGR, in water and in water/trifluoroethanol (TFE). Exchange contributions, R(ex), to spin-spin relaxation rates for (13)C(alpha) and (13)C(beta) groups were derived and were ascribed to be mainly due to peptide folding-unfolding. To evaluate the exchange time, tau(ex), from R(ex), the chemical shift difference between folded and unfolded states, Deltadelta, and the populations of these states, p(i), were determined from the temperature dependence of (13)C chemical shifts. For both peptides, values for tau(ex) fell in the 1 micros to 10 micros range. Under conditions where the peptides are most folded (water/TFE, 5 degrees C), tau(ex) values for all residues in each respective peptide were essentially the same, supporting the presence of a global folding-unfolding exchange process. Rounded-up average tau(ex) values were 4 micros for the helix peptide and 9 micros for the hairpin peptide. This 2-3-fold difference in exchange times between helix and hairpin peptides is consistent with that observed for folding-unfolding of other small peptides.     

Temperature dependence of mammalian muscle contractions and ATPase activities

Isolated rat and mouse extensor digitorum longus (EDL) and soleus muscles were studied under isometric and isotonic conditions at temperatures from approximately 8 degrees -38 degrees C. The rate constant for the exponential rise of tension during an isometric tetanus had a Q10 of approximately 2.5 for all muscles (corresponding to an enthalpy of activation, delta H = 66 kJ/mol, if the rate was determined by a single chemical reaction). The half-contraction time, contraction time, and maximum rate of rise for tension in an isometric twitch and the maximum shortening velocity in an isotonic contraction all had a similar temperature dependence (i.e., delta H approximately 66 kJ/mol). The Mg++ ATPase rates of myofibrils prepared from rat EDL and soleus muscles had a steeper temperature dependence (delta H = 130 kJ/mol), but absolute rates at 20 degrees C were lower than the rate of rise of tension. This suggests that the Mg++ ATPase cycle rate is not limiting for force generation. A substantial fraction of cross-bridges may exist in a resting state that converts to the force-producing state at a rate faster than required to complete the cycle and repopulate the resting state. The temperature dependence for the rate constant of the exponential decay of tension during an isometric twitch or short tetanus (and the half-fall time of a twitch) had a break point at approximately 20 degrees C, with apparent enthalpy values of delta H = 117 kJ/mol below 20 degrees C and delta H = 70 kJ/mol above 20 degrees C. The break point and the values of delta H at high and low temperatures agree closely with published values for the delta H of the sarcoplasmic reticulum (SR) Ca++ ATPase. Thus, the temperature dependence for the relaxation rate of a twitch or a short tetanus is consistent with that for the reabsorption rate of Ca++ into the SR.     

Minimal levels of cold-adaptation in postsynaptic currents of a subantarctic teleost, <Emphasis Type="Italic">Notothenia rossii</Emphasis> (Perciformes: Notothenioidei: Nototheniidae)

As a part of the ICEFISH04 project on the RVIB Nathaniel B. Palmer, miniature end plate currents (MEPCs) were recorded from the extraocular muscles of Notothenia rossii captured at King Edward Point, South Georgia. A total of 1,176 MEPCs were recorded from the inferior oblique extraocular muscles of four specimens, over a temperature range of 1–12°C. The MEPCs were normal in form, with a rapid quasi-linear increase in inward current (typically <500 μs), followed by a slower exponential decay of the inward current to baseline. Exponential decay rates were calculated for individual MEPCs by linear regression of the log-transformed data, and converted to exponential time constants (τ). Only those MEPCs that fit the exponential model well, with r ² ≥ 0.95 (or in some cases r ² ≥ 0.99) were used for further calculations. At temperatures between 1 and 2°C, τ ranged from about 2,000 to 4,000 μs, similar to values extrapolated for temperate teleosts at the same temperature, but significantly longer than τ from MEPCs of high-latitude Antarctic nototheniids. Between 11 and 12°C, τ values for the N. rossii MEPCS were mainly between 1,100 and 1,700 μs, giving a Q ₁₀ of 2.05. An Arrhenius plot and linear regression were used to describe the effect of changing temperature on the decay phase of the N. rossii MEPCs: −ln τ = 27.887−6078/K, yielding an Arrhenius temperature coefficient (μ or apparent E _a) of −50.5 ± 2.9 (95% CL) kJ mol⁻¹ deg⁻¹. When compared with other nototheniids, these results showed that the neuromuscular junctions of N. rossii are compensated for low temperature, but not to the same degree as those of high Antarctic species. The ICEFISH Cruise (International Collaborative Expedition to collect and study Fish Indigenous to Sub-antarctic Habitats) was conducted on board the RVIB Nathaniel B. Palmer in May to July 2004. For further information, please visit .     

Kinetic studies on the helix-coil transition of fluorescent labeled poly(-L-lysine) by the temperature-jump technique

Fluorescent dansyl labels were covalently attached to poly (L-lysine) (poly(Lys)) with a degree of polymerization of 300 to 600. The degree of labeling was 0.01 to 0.085 (mol label to mol amino acid residues). From the decay of the anisotropy of fluorescence it was concluded that the labels were highly mobile both in the coiled and helical state. A decrease of fluorescence intensity accompanied the helix-coil transition. Identical pH induced transition curves were measured by circular dichroism and fluorescence. The midpoint of the transition was at pH 10.2. The kinetics of the transition were studied by temperature-jump relaxation using fluorescence detection. A single relaxation phase was observed. The relaxation time tau exhibited a distorted bell shaped dependence on the degree of helicity f with a maximum value tau(max) = 15 micros at f = 0.3 and 20 degrees C. It was independent of polymer concentration and of the degree of labeling. A rate constant of helix propagation kF = 10(7) s(-1) was calculated from tau(max) and published values of the nucleation parameter sigma. The activation energy was 16 kJ mol . The observed rate constant is comparable to that of poly(L-glutamic acid) but two orders of magnitude smaller than that found for polyamino acids with nonionizable side chains.     

Temperature dependence and acclimatory response of amylase in the High Arctic springtail Onychiurus arcticus (Tullberg) compared with the temperate species Protaphorura armata (Tullberg)

Amylolytic activity was measured in whole body homogenates of High Arctic (Onychiurus arcticus) and temperate (Protaphorura armata) springtails (Collembola: Onychiuridae) in the temperature range 5-55 degrees C. A pH of ca. 8 was optimum for amylolytic activity in both species. A higher weight-specific amylolytic activity was observed in P. armata. In O. arcticus, amylolytic activity depended on thermal acclimation, which increased during 2 and 9 weeks of cold acclimation (5 degrees C) and decreased over 7 weeks of warming (15 degrees C) of animals that were previously acclimated to cold for 2 weeks. In cold-acclimated O. arcticus, a slower decrease of amylolytic activity occurred with lowering of temperature in the range 5-20 degrees C in comparison with warm-acclimated specimens and P. armata, which resulted in higher activity at 5 degrees C. The activation energy calculated from an Arrhenius plot for P. armata was 68.7 kJ.mol(-1). In O. arcticus it was between 30.2 and 61.5 kJ.mol(-1), being lower in cold-acclimated samples. The temperature optimum for amylolytic activity was higher in the temperate species (40 degrees C), whilst in O. arcticus it depended on the acclimation regime: it rose to 35 degrees C after warm acclimation and decreased to 20 degrees C after cold adaptation. The total soluble protein content of body tissues of O. arcticus also increased during cold acclimation. These differences between the two species suggest that amylolytic activity is an indicator of cold adaptation in the High Arctic O. arcticus.     

Voltage-dependent calcium channels in ventricular cells of rainbow trout: effect of temperature changes in vitro

Voltage-dependent calcium channels (VDCC) in ventricular myocytes from rainbow trout (Oncorhynchus mykiss) were investigated in vitro using the perforated patch-clamp technique, which maintains the integrity of the intracellular milieu. First, we characterized the current using barium as the charge carrier and established the doses of various pharmacological agents to use these agents in additional studies. Second, we examined the current at several physiological temperatures to determine temperature dependency. The calcium currents at 10 degrees C (acclimation temperature) were identified as L-type calcium currents based on their kinetic behavior and response to various calcium channel agonists and antagonists. Myocytes were chilled (4 degrees C) and warmed (18 and 22 degrees C), and the response of VDCC to varying temperatures was observed. There was no significant dependency of the current amplitude and kinetics on temperature. Amplitude decreased 25-36% at 4 degrees C (Q(10) approximately 1.89) and increased 18% at 18 degrees C (Q(10) approximately 1.23) in control, Bay K8644 (Bay K)-, and forskolin-enhanced currents. The inactivation rates (tau(i)) did not demonstrate a temperature sensitivity for the VDCC (Q(10) 1.23-1. 92); Bay K treatment, however, increased temperature sensitivity of tau(i) between 10 and 18 degrees C (Q(10) 3.98). The low Q(10) values for VDCC are consistent with a minimal temperature sensitivity of trout myocytes between 4 and 22 degrees C. This low-temperature dependency may provide an important role for sarcolemmal calcium channels in adaptation to varying environmental temperatures in trout.     

Slow charge movement in mammalian skeletal muscle

Voltage-dependent charge movements were measured in the rat omohyoid muscle with the three-microelectrode voltage-clamp technique. Contraction was abolished with hypertonic sucrose. The standard (ON-OFF) protocol for eliciting charge movements was to depolarize the fiber from -90 mV to a variable test potential (V) and then repolarize the fiber to -90 mV. The quantity of charge moved saturated at test potentials of approximately 0 mV. The steady state dependence of the amount of charge that moves as a function of test potential could be well fitted by the Boltzmann relation: Q = Qmax/(1 + exp[-(V - V)/k]), where Qmax is the maximum charge that can be moved, V is the potential at which half the charge moves, and k is a constant. At 15 degrees C, these values were Qmax = 28.5 nC/microF, V = -34.2 mV, and k = 8.7 mV. Qmax, k, and V exhibited little temperature dependence over the range 7-25 degrees C. "Stepped OFF" charge movements were elicited by depolarizing the fiber from -90 mV to a fixed conditioning level that moved nearly all the mobile charge (0 mV), and then repolarizing the fiber to varying test potentials. The sum of the charge that moved when the fiber was depolarized directly from -90 mV to a given test potential and the stepped OFF charge that moved when the fiber was repolarized to the same test potential had at all test potentials a value close to Qmax for that fiber. In nearly all cases, the decay phase of ON, OFF, and stepped OFF charge movements could be well fitted with a single exponential. The time constant, tau decay, for an ON charge movement at a given test potential was comparable to tau decay for a stepped OFF charge movement at the same test potential. Tau decay had a bell-shaped dependence on membrane potential: it was slowest at a potential near V (the midpoint of the steady state charge distribution) and became symmetrically faster on either side of this potential. Raising the temperature from 7 to 15 degrees C caused tau decay to become faster by about the same proportion at all potentials, with a Q10 averaging 2.16. Raising the temperature from 15 to 25 degrees C caused tau decay to become faster at potentials near V, but not at potentials farther away.(ABSTRACT TRUNCATED AT 400 WORDS)     

Temperature dependency of cupular mechanics and hair cell frequency selectivity in the fish canal lateral line organ

The mechanical frequency selectivity of the cupula located in the supraorbital lateral line canal and the frequency selectivity of the hair cells driven by the cupula were measured simultaneously in vivo. Laser interferometry was used to measure cupular mechanics and extracellular receptor potentials were recorded to determine hair cell frequency selectivity. Results were obtained from two teleost fish species, the ruffe (Acerina cernua L.), a European temperate zone freshwater fish, and the tropical African knife fish (Xenomiystus nigri). In both species cupular displacement grows with increasing frequency of canal fluid displacement, reaching a maximum at 115 Hz in the ruffe and at 460 Hz in the African knife fish. Cupular best frequencies were independent of temperature. Cut-off frequencies of hair cell frequency selectivity were found to depend on temperature with a Q10 of 1.75, ranging from 116 Hz (4 degrees C) to 290 Hz (20 degrees C), as established in the ruffe. At normal habitat temperatures of the two fish species (ruffe, 4 degrees C; African knife fish, 28 degrees C), this results in hair cell cut-off frequencies that match the two different cupular best frequencies remarkably well. This match suggests adjusted signal transfer in these two peripheral stages of canal lateral line transduction.     

Two-state equilibria of myosin subfragment 1 and its complexes with ADP and actin

We previously reported that the nucleotide complex of myosin subfragment 1, S1.epsilon ADP, exists in two states on the basis of the temperature dependence of the fluorescence decay of bound 1,N6-ethenoadenosine diphosphate (epsilon ADP) [Aguirre, R., Lin. S.-H., Gonsoulin, F., Wang, C.-K., & Cheung, H.C. (1989) Biochemistry 28, 799-809]. We have extended the previous study of the equilibrium between the two states, S1L.ADP in equilibrium S1H.ADP, by using a fluorescently labeled myosin S1 (S1-AF). In S1 alkylated with IAF [5-(iodoacetamido)fluorescein], the decay of the label emission was biexponential both in the presence and absence of ADP and/or actin. In the presence of ADP, the two decay times were 4.30 (alpha 1 = 0.55) and 0.80 ns (alpha 2 = 0.45) at 12.4 degrees C, in a medium containing 60 mM KCl, 30 mM TES (pH 7.5), and 2 mM MgCl2. The steady-state fluorescence intensities of S1-AF, (S1-AF).ADP, acto.(S1-AF), and acto.(S1-AF).ADP were dependent on temperature over the range of 5-30 degrees C. By combining lifetime and steady-state intensity data, we obtained for the two-state transition (S1-AF)L.ADP in equilibrium (S1-AF)H.ADP the following parameters: delta H degrees = 16.1 kcal/mol (67.3 kJ/mol) and delta S degrees = 55.8 cal/(deg.mol) [233.5 J/(deg.mol)], in agreement with previous results obtained with epsilon ADP. The delta H degrees values for the two-state transition of S1-AF, acto.(S1-AF), and acto.(S1-AF).ADP are 13.0, 21.6, and 5.2 kcal/mol, respectively. The corresponding delta S degrees values are 46.9, 79.5, and 17.4 cal/(deg.mol).(ABSTRACT TRUNCATED AT 250 WORDS)     

Electrophysiological aspects of synaptic transmission at the electromotor junction of Torpedo marmorata

Miniature and stimulus-evoked electroplaque potentials were recorded in Torpedo electrocytes intracellularly and extracellularly and analysed quantitatively. Tetrodotoxin reversibly blocked stimulus evoked potentials but hardly affected spontaneous miniature potentials in amplitude and frequency. The quantum content of stimulus-evoked potentials varied between 150 and 400 in normal saline and decreased in low Ca2+ high Mg2+ solution. Quantal release conformed to binomial statistics and allowed determination of the release parameters p and n. Analysis of the time constant of decay of spontaneous miniature electroplaque currents showed variation around a mean of 0.75 +/- 0.16 msec (SD) which was greatly prolonged by application of neostigmine.     

Thermoregulatory behavior of the triggerfish Balistes fuscus in an electronic shuttlebox

Ten blue triggerfish,Balistes fuscus, were tested individually for 3 days each in Ichthyotron electronic shuttleboxes to measure their thermoregulatory behavior. The modal thermal preferendum, a species-specific measure of temperature preference which is independent of prior thermal acclimation, was 25 °C. The triggerfish voluntarily occupied a 16–27 °C range of temperature, out of a potentially available range of 0–50 °C. There was no significant difference in preferred temperature between night and day, indicating lack of a thermoregulatory rhythm in this species. The preferred temperature range of this tropical marine reef species is similar to that of cool temperate freshwater and marine fishes; many warm temperate species prefer higher temperatures.     

Enzymatic capacities for beta-oxidation of fatty fuels are low in the gill of teleost fishes despite presence of fatty acid-binding protein.

A variety of circulating fuels can support the work of the teleost gill. Previous work indicates, however, that unlike other aerobic tissues from teleosts, the gill may have a limited capacity to oxidize fatty fuels. We determined capacities for catabolism of carbohydrate, fatty acids, and amino acids in four species of temperate marine or euryhaline teleosts representing distinct lineages. In addition, we assessed the capacity for fatty acid oxidation in the gill from an Antarctic species. Activities of rate-limiting or regulatory enzymes from pathways of energy metabolism were measured at physiological temperatures (15 degrees or 1 degrees C). In the temperate species, ATP yields from glucose are 3- to 30-fold greater (varying with species) than ATP yields from a monounsaturated fatty acid, while ATP generation from glutamate is 2-50 times greater than similar capacities for the lipid fuel. Like the temperate species, capacity for beta-oxidation of fatty acids is limited in the Antarctic species. A positive linear correlation between activities of citrate synthase (central pathway of oxidative metabolism) and hexokinase (glycolysis) adds further support to the hypothesis that glucose is a preferred metabolic fuel in gill. Our results also demonstrate that fatty acid-binding protein is present in the gill of teleost fishes. It is likely that this protein plays a more important role facilitating anabolic pathways in lipid metabolism rather than fatty acid oxidation in the gill of teleost fishes.